The present invention relates generally to apparatus for determining the weight of a vehicle while it is in motion. More particularly the invention relates to such apparatus which determines the vehicle weight by measuring the seismic vibrations produced as a vehicle moves over a roadbed.
The advent of electronic screening systems brings with it the need for a low-cost, dependable weigh-in-motion system that can function successfully on the mainline.
The vibrations in the highway pavement represents a detectable seismic signal. The variance of this signal is proportional to truck weight. If the speed of the truck and distance from the truck to the seismic detector of the present invention, Seismic Weigh-In-Motion system are known, the weight of the truck is directly measurable. The Seismic Weigh-In-Motion system is hereinafter referred to as the SWIM system. The seismic weigh-in-motion system of the present invention in its most basic format is an off-pavement screening system that utilizes seismic signals (generated as the vehicle travels on the mainline at up to highway speeds) to determine truck weights.
Devices which disclose the use of electronic screening systems to target a moving vehicle are set forth in the following United States patents, namely: U.S. Pat. No. 4,337,528 to Clinard et al.; U.S. Pat. No. 4339,010 to Malikov et al.; U.S. Pat. No. 4,539,650 to Griffin; U.S. Pat. No. 4,957,178 to Milk; U.S. Pat. No. 4,712,423 to Siffert; and, U.S. Pat. No. 4,560,016 to Ibanez.
U.S. Pat. No. 4,337,528 discloses an electronic screening system which provides seismic detection of a target and uses a geophone to detect earth vibrations caused by actions of a target such as a moving vehicle. The vibrations are wideband amplified and band-passed filtered with pass banks being fed to threshold detectors. The output of the threshold detectors are fed to a diode AND logic circuit, the output thereof indicating the presence of a target, such as a vehicle. Only the presence of such a target is available from this screening system.
All of the remaining patents to Malikov (U.S. Pat. No. 4,339,010), Griffin (U.S. Pat. No. 4,539,650), Milk (U.S. Pat. No. 4,957,178), Seifert (U.S. Pat. No. 4,712,423) and Ibanez (U.S. Pat. No. 7,560,016) are directed to electronic screening systems which are utilized for weighing transport vehicles in motion; however, each of these patents describe an intrusive screening system which requires the use of some type of bending or flexure member which must bend or flex under the weight of the moving vehicle to provide an output signal which is proportional to the amount of bending or flexure. Such intrusive systems are subjected to mechanical failure due to extensive flexing or bending of the member, thereby, requiring an undue amount of maintenance.
A Lawrence Livermore National Laboratory (LLNL) report entitled xe2x80x9cA Seismic Weigh-In-Motion Method for Weight Estimation of Vehicles on the Highwayxe2x80x9d authored by F. Dowler, D. Lager, and M. Barth was printed in January, 1993. The report is an informal report intended for internal or limited external distribution and was not released outside LLNL until November 1999. The report represents a preliminary treatment of the concept of weighing a vehicle in motion by means of a seismic signal.
Whenever in motion a truck encounters rolling resistance. In overcoming such resistance and in interacting with the ground through vertical oscillations, the truck transfers a considerable amount of energy into the ground. Some portion of this energy is reflected back into the atmosphere, but a sizeable fraction takes the form of short-period (SP) seismic vibrations, with the remainder transformed into thermal energy.
In the present inventive concept, the seismic source is located on the air-ground interface, and only surface waves appear to be of interest, so far as short-period vibrations are concerned. Surface waves generally are divided into Love waves, which exhibit secondary horizontal (SH) wave motion, and Rayleigh waves, which are a combination of primary (P) and secondary vertical (SV) type waves. The SWIM system of the present invention detects both Rayleigh and Love waves.
The present seismic detection system will normally be deployed as part of a permanent weighing/inspection installation but may be deployed as a portable unit, if desired. The SWIM system screens for vehicle-produced, in-ground (seismic) signals produced by heavy trucks that are traveling on mainline pavements at highway speeds. Vehicles exceeding prescribed parameters would be instructed to pull into the weigh station or inspection area to be weighed on static scales (platform, portable, etc.). Pull-in instructions would be by means of either in-cab transponders and/or dedicated visual external weigh station signals/signs.
On multi-lane highways such as interstate highway routes trucks would be required to use the right-hand (outside) lane. Additionally, trucks would be required to maintain a constant speed which would be consistent with the posted speed limit for that portion of the highway. Where needed and depending largely on roadway surface condition, positive lane definition would be achieved through the use of transverse slots or rumble slips installed on the pavement surface in the designated lane in advance of the SWIM sensor unit. These strips or slots, through their inherent characteristic of initiating vibration in the passing vehicle, would be tuned to provide a unique signature to aid in the speed and identification of a specific vehicle. An added benefit of installing rumble strips or slots would be to help eliminate concern over registering heavier, but inappropriate, target vehicles such as buses and motor homes traveling in adjacent lanes.
An efficient, rapid, and accurate system for weighing trucks while the trucks are in motion is provided by the seismic weigh-in-motion system of the present invention.
The seismic weigh-in-motion system includes a seismic sensor system which is mounted adjacent (off pavement) of the highway prior to the point at which the truck enters the deceleration lane at a truck weighing station. The sensor senses seismic vibrations transmitted into the ground by the moving truck. Signals indicative of these vibrations are transmitted through a fiber optic cable to a seismic weigh-in-motion processor mounted inside the weighing station.
This vibration signal along with the speed of the truck , (determined by speed detecting devices as described hereinbelow) as it passes the sensor system is processed in the processor to provide an output thereof which is indicative of the weight of the truck. Additional components such as a soil temperature measuring device and a soil moisture content measuring device may be mounted at the sensor system in contact with or imbedded in the ground to provide information indicative of soil temperatures and soil moisture content through the fiber optics cable to the processor in the weighin-station.
It is therefore an object of the present invention to provide an electronic screening system for weighing moving vehicles, such as trucks while the vehicles or trucks are in motion.
It is a further object of the present invention to provide such an electronic screening system in which the vibrations of the truck, as it moves along a highway, are sensed and processes, and, signals representative of the amplitude and frequency of the vibrations are coupled with the measured speed of the moving truck to produce an output indicative of the truck weight.